The present invention relates generally to Radio Frequency (RF) and microwave technology, and more specifically to the measurement and processing of signal data of a device-under-test under different impedance load conditions.
Telecommunication appliances like portable phones have been widely adopted by the general public. Just like Local-Multipoint Distribution Service, Wireless LAN, and Wideband CDMA, for example, these appliances rely heavily on microwave technology and contain such microwave components like mixers, low-noise amplifiers, power amplifiers, etc.
It turns out in practice that the design of power amplifiers often is one of the toughest problems to solve. Typically this requires several design iterations, the main reason being the limited accuracy of the RF transistor models used, especially with respect to the description of the non-linear behavior thereof.
Currently, transistor models for power amplifier design are based on DC, CV and/or S-parameter measurements. They can be either technology-dependent analytical models, such as Curtice Cubic, Materka, Statz, Tajima, BSIM, MM9, VBIC, and others, or measurement based such as HP-Root.
However, these models all are based on small signal measurements, whereas they are used in non-linear (large-signal) operation. Hence, one can expect that these models not always perform well in describing the hard non-linear behavior of a device-under-test like, for example, an RF power transistor. For these type of applications it is suggested to use so-called xe2x80x9cnon-linear scattering functions,xe2x80x9d or more generally the describing function, which can be considered an extension of the S-parameters formalism into hard non-linear behavior. Like S-parameters for the linear behavior, the describing function is a characteristic of the device and is independent on the (type of) measurement system that was used to measure it.
It is an object of the present invention to provide a novel apparatus for collecting RF signal measurement data at signal ports of an RF and microwave device-under-test, generally for characterizing the non-linear behavior of the device in a mismatched load environment, and in particular for performing measurements for extracting the non-linear scattering functions of a device-under-test.
It is a further object to provide a Non-linear Network Measurement System (NNMS) arranged for non-linear signal data acquisition of a device-under-test in accordance with the present invention.
According to the present invention, in a first aspect thereof, there is provided an apparatus for collecting RF signal measurement data at signal ports of an RF and microwave device-under-test, the apparatus comprising means for measuring incident and reflected RF signals at the signal ports, synthesizer means for generating RF signals at a fundamental frequency and higher harmonics of the fundamental frequency, tuner means arranged for loading the device-under-test under different impedance conditions for the fundamental frequency and the higher harmonics, and means for feeding the RF signals of the synthesizer means to the signal ports of the device-under-test.
The apparatus according to the invention provides for a novel data collection at the signal ports of a device-under-test providing a tunable impedance match for both the fundamental frequency and higher harmonics RF signals. Thereby combining passive and active harmonic loadpull measurements into one apparatus for extracting non-linear scattering functions of a device-under-test.
In an embodiment of the invention the apparatus comprises first synthesizer means, for generating the RF signals at the fundamental frequency, and second synthesizer means, for generating the higher harmonics RF signals, wherein the first and second synthesizer means connect to the signal ports of the device-under-test by diplexer means.
By connecting, in accordance with a further embodiment of the apparatus according to the invention, the second synthesizer means to the diplexer means by switching means, and by arranging the switching means for connecting the second synthesizer means to selected ones or all of the signal ports of the device-under-test, the higher harmonics can be selectively injected at one or a plurality of the signal ports of the device. This provides a maximum of measurement flexibility.
For varying the impedance match conditions of the synthesizers at the signal ports of the device, in a further embodiment of the invention, the first synthesizer means connect to the diplexer means by the tuner means.
In a still further embodiment of the invention, the second synthesizer means connect to the diplexer means in an impedance matched manner, such that the higher harmonics are injected under matched conditions. This contributes to the accuracy of the measurements, because in practice higher harmonics up to five times the fundamental frequency may be applied.
In order to even further enhance the accuracy of the measurement, in another embodiment of the invention, the first synthesizer means connect to the tuner means by means for terminating the higher harmonics.
Preferably, means for biasing the device-under-test connect by the tuner and diplexer means to the signal ports of the device-under-test.
For collecting and processing the measurement data a commercially available Non-linear Network Measurement System (NNMS), such as provided by Agilent Technologies, is used for data collecting, i.e. data acquisition and processing for extracting the non-linear scattering functions for characterizing the non-linear RF signal behavior of the device-under-test.
The invention further relates to an arrangement comprising synthesizer means for generating RF signals at a fundamental frequency and higher harmonics of the fundamental frequency, tuner means arranged for loading the device-under-test under different impedance conditions for the fundamental frequency and the higher harmonics, and means for feeding the RF signals of the synthesizer means to the signal ports of the device-under-test.
The invention also provides a modified Non-linear Network Measurement System (NNMS) enhanced by the arrangement disclosed above, for providing a single integrated apparatus for performing the measurements according to the present invention, as much as possible in an automated manner.
The above-mentioned and other features and advantages of the invention are illustrated in the following detailed description with reference to the enclosed drawings.